A known evaluation method for evaluating a flow rate of a fluid coming from a tank comprises measuring a level of the fluid in the tank. In simple circumstances, e.g. assuming that the level measurement is continuously available, that the tank is cylindrical in shape, and that fluid does not accumulate anywhere between the outlet from the tank and the point at which the flow rate is evaluated, then the fluid flow rate can be evaluated with certainty merely by using an affine function.
Nevertheless, in practice, the measurement of the fluid level is rarely continuously available, which means that it is necessary to make use of interpolations or of estimators during periods when the level measurement is unavailable. However, uncertainties and biases can exist in association with level measurements and/or with the estimators used. Furthermore, the tank may be of non-cylindrical shape, thereby introducing nonlinearity into the evaluation function. There therefore exists a need for a novel type of method of evaluating a flow rate.